The invention relates to a process for preparing alkanesulfonyl chlorides by reacting alkanethiols and/or dialkyl disulfides with chlorine and water.
Alkanesulfonyl chlorides having 1-12 carbon atoms are used in large quantities as starting materials and intermediates for organic syntheses, for example of plant protection agents or photographic color developers. Various processes for their preparation, including preparation on an industrial scale, are known, and amongst these the synthesis from alkanethiols or dialkyl disulfides by reaction with chlorine and water is preferred. The disadvantages of this known, batchwise process are the as yet unsatisfactory yields, a purity of the reaction products which is insufficient for many applications, and the need to use mechanical stirring equipment.
In addition, a process for the continuous preparation of alkanesulfonyl chlorides, in which alkanethiols or dialkyl disulfides, in concentrated aqueous hydrochloric acid, are reacted with chlorine in a circulatory reactor, is known from German Offenlegungsschrift No. 1,811,768. The requisite intensive mixing of the reactants is in that case effected by the hydrogen chloride formed during the reaction. The alkanesulfonyl chloride, which is of greater specific gravity, separates out from the aqueous hydrochloric acid serving as the reaction medium as soon as the latter has become saturated therewith at the reaction temperature. To permit sufficiently rapid separating-out, a part of the hydrochloric acid saturated with the alkanesulfonyl chloride must be drawn off intermittently or continuously and replaced by water or fresh hydrochloric acid. Herein resides a substantial disadvantage of this known process, since some dissolved alkanesulfonyl chloride is drawn off with the hydrochloric acid and can only be isolated therefrom by an expensive work-up. In the preparation of methanesulfonyl chloride, about 10 percent by weight of the reaction medium drawn off is methanesulfonyl chloride. If such isolation is dispensed with, the yield, and hence also the economy of the process, is diminished. Furthermore, increased effort is then needed for detoxification, in the interest of protecting the environment.